Voltage variation in unbalanced three phase loads.
Too long since I studied this in school, so I need some help. I do sound and for regional concerts/corporate events. We normally tie in to house power or a generator with 4o or 2o cable with cam lock connectors. Very common in our industry. These feed a three phase power distro (Motion Labs) which feeds racks and other equipment through L14-6 and Edison 20A connections.
In one of the venues we work locally I have had severe problems with supply voltage variations when the load was unbalanced. The last situation was a relatively small PA and we also fed power to the Video guys. Current draws were on the order of 28A-17A-9A for the three phases. One of the phases was down to around 100V.
The in-house people said that it was not their system, and the variation was because of the unbalanced load. We shut everything off and shuffled power around and achieved a load that was very close to balanced (can't ever be because the draw from the PA is always varying).
My position is that a 200A service should not sag that much with only what I consider a small imbalance in load.
Sorry about the long question, but I tried to lay out the whole situation. Thanks!
